The present invention relates to electrical fuses and, more particularly, to plug-in fuses with simplified methods to determine fuse condition.
Electrical fuses provide reliable and economical protection for electrical wiring and components. Because of their small size and low cost, plug-in fuses have found wide use in industrial and consumer products such as automobiles, aircraft, air conditioning and heating equipment.
Due to the complexity of such applications, manufacturers often utilize fuse blocks or holders having multiple fuse receptacles. In order to minimize space requirements, fuse receptacles are densely packed, allowing minimal space for inspection, insertion and removal of the fuses. Component packaging often dictates placement of the fuse holders in inaccessible areas, increasing the problem of accessing individual fuses for troubleshooting, testing, and replacement.
In the past, inspection of a fuse to determine its condition required removal of the fuse and subsequent testing of the fuse with a meter such as a volt-ohm meter. The removal, testing and re-insertion of a fuse, especially if the fuse holder is in an inconvenient location, can become a tedious chore, increasing the time and cost for troubleshooting and repair of equipment. Close spacing of fuses often requires use of a tool to aid in the removal and/or insertion of the fuse. Such requirement for specialized tools and equipment prevents inexperienced users from performing an otherwise simple task.
Various fuse designs have been introduced to address the problem of inspecting the condition of a fuse, and to make the fuse easier to remove and re-install. U.S. Pat. No. 4,604,602 discloses a plug-in fuse with an overhanging upper portion to improve grasping of the fuse. U.S. Pat. No. 4,670,729 discloses a plug-in fuse with a transparent case to allow visual determination of the condition of the fuse link. U.S. Pat. No. 4,308,516 discloses a plug-in fuse with a high-resistance, heat responsive member which changes color upon heating. U.S. Pat. No. 5,598,138 discloses a fault-indicating blade fuse utilizing a LED or incandescent bulb which lights upon opening of the fuse element.
Despite a significant number of fuse designs introduced, there remains a significant need for improvement in fuse condition monitoring and fuse removal/insertion features.
Therefore an object of the present invention is to provide a plug-in fuse which can be easily removed and inserted into a high-density fuse holder without the need for special tools or equipment.
A further object of the present invention is to provide a plug-in fuse for automotive, aircraft, industrial equipment and consumer equipment with multiple means to quickly determine the fuse condition without special tools or equipment.
A further object of the present invention is to provide a plug-in fuse which utilizes the heat produced by the burnout of the burnout portion to produce a visual indication of fuse condition.
A further object of the present invention is to provide a plug-in fuse which utilizes the heat produced by the burnout of the burnout portion to produce a tactile indication of fuse condition.
A further object of the present invention is to provide a plug-in fuse with a transparent body to provide a visual indication of fuse condition.
Another object of the present invention is to provide a fuse in which the condition can be determined, and replacement made if necessary, by a person of limited experience.
The fuse of the current invention comprises a fusible link or burnout portion, and at least two terminals connected to the burnout portion by connecting portions. The burnout portion is enclosed in a fuse body and the two terminals extend from the bottom of the fuse body in the preferred embodiments. The shape of the fuse body is necked between the top and bottom of the fuse body by a side-indented portion on each side of the fuse. The side-indented portions provide grip surfaces for the thumb and finger of a hand. Side-extended portions above and below the side-indented portions provide ledge surfaces which allow push forces to be exerted by the thumb and finger to insert the fuse in a fuse holder, and for pull forces to be exerted by the thumb and finger to remove the fuse from the holder. Similarly, the front and back faces of the fuse may be necked to allow gripping of the fuse body by the faces.
In the preferred embodiments, the top portion of the fuse contains a heat or temperature-responsive material in close proximity to the burnout portion. Heat from burnout of the burnout portion conducted to the temperature-responsive material raises the temperature of the temperature-responsive material sufficiently to provide visual and/or tactile changes in the temperature-responsive material. The temperature-responsive material may be disposed as a layer on the upper portion of the body or, alternatively, the upper portion of the body, a substantial portion, or the entire body may be made of the temperature-responsive material. In other embodiments, the burnout portion may be in contact with the temperature-responsive material. In still other embodiments, a heat-conductive material may be disposed between the burnout portion and the temperature-responsive material. In the preferred embodiments, the body portions comprising the temperature-responsive materials are on the top of the fuse, or another external surface of the fuse which is easily seen, and/or felt by, a user when installed.
The temperature-responsive material may be a material which degrades to produce tactile changes on the surface of the body of the fuse. Or, the temperature-responsive material may be a material which decomposes to form discolored gaseous or particulate products observable in a chamber enclosing the burnout portion of the fuse element.
In the preferred embodiments, a cavity in the body encloses the burnout portion. The body of the fuse is made of a transparent or translucent material to allow visual observation of the condition of the burnout portion or discolored burnout components or gas. External electrical contacts, connected to the connecting portions of the burnout portion, allow electrical testing of the fuse without removal of the fuse from the fuse holder.